Answer to U2 Soundcheck of Leonard Cohen song...

A recent fan noted that U2 did a soundcheck for a Leonard Cohen song, well it looks like this is why they did it:

From Gigwise: by Scott Colothan on 5/20/2005

U2 made a special intimate appearance yesterday in New York by playing as the backing band for legendary songwriter Leonard Cohen. The Irish supergroup were filmed recording the Cohen track 'Tower of Song' at the erotic cabaret lounge The Slipper Club for a forthcoming documentary about the singer, reports Contactmusic. On the song, Bono took over vocal duties on one verse while the rest of the band played back-up.
It's not the first time Bono has paid tribute to Cohen. He covered the Cohen classic 'Hallelujah' for the tribute album 'Tower Of Song' in 1995.
Also paying tribute to Leonard Cohen on the Lian Lunson documentary are The Edge, Jarvis Cocker and Nick Cave.